When fine-sized 45ZnO·55P2O5 or 50ZnO·50P2O5 glass powders were mixed with distilled water, hydration immediately occurred, resulting in the formation of viscous hydrogels. 31P MAS-NMR spectra showed that the hydrogels contain orthophosphates and long-chain phosphates; no significant differences in their structures between the hydrogels were shown. The 45ZP gel and 50ZP gel showed high conductivities (e.g., 9.9 and 2.8 mS/cm, respectively, at 30°C). The conductivities were related to the proton amount in the hydrogel; the amount in the 45ZP gel was larger than that in the 50ZP gel. Electric double-layer capacitors (EDCs) were prepared using electrolytes consisting of the hydrogels. The specific capacities of the EDC cell for the 45ZP gel and 50ZP gel were 2.40 and 2.06 F/g, respectively. The possibility as an EDC electrolyte may be related to proton conductivities of the hydrogels.